<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .a{
            background:#00ffff ;
        }
    </style>
</head>
<body>
<table width="60%" border="1">
    <tr>
        <td class="a" colspan="3">a</td>
    </tr>
    <tr>
        <td>4</td>
        <td>5</td>
        <td>6</td>
    </tr>
    <tr>
        <td>7</td>
        <td>8</td>
        <td>9</td>
    </tr>
</table>
</body>
</html>